[Bug 2072858] Re: Fix L2CAP/LE/CPU/BV-02-C bluetooth certification failure

This bug is awaiting verification that the linux-nvidia-
tegra-5.15/5.15.0-1030.30~20.04.1 kernel in -proposed solves the
problem. Please test the kernel and update this bug with the results. If
the problem is solved, change the tag 'verification-needed-focal-linux-
nvidia-tegra-5.15' to 'verification-done-focal-linux-nvidia-tegra-5.15'.
If the problem still exists, change the tag 'verification-needed-focal-
linux-nvidia-tegra-5.15' to 'verification-failed-focal-linux-nvidia-
tegra-5.15'.


If verification is not done by 5 working days from today, this fix will
be dropped from the source code, and this bug will be closed.


See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how
to enable and use -proposed. Thank you!


** Tags added: kernel-spammed-focal-linux-nvidia-tegra-5.15-v2 verification-needed-focal-linux-nvidia-tegra-5.15

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https://bugs.launchpad.net/bugs/2072858

Title:
Fix L2CAP/LE/CPU/BV-02-C bluetooth certification failure

Status in OEM Priority Project:
New
Status in linux package in Ubuntu:
Invalid
Status in linux source package in Jammy:
Fix Released
Status in linux source package in Noble:
Fix Released

Bug description:
SRU Jusitification for Kernel

[Impact]

Noble failed the L2CAP/LE/CPU/BV-02-C test in the Porfile Tuning Suite
(PTS), which Jammy previously could pass.

This is due to new behavior introduced in
e4b019515f950b4e6e5b74b2e1bb03a90cb33039 (Bluetooth: Enforce
validation on max value of connection interval). The kernel only
accept Connection Parameter Update Requests whose incoming
conn_max_interval are lower than the current conn_max_interval, and
adjust the newer conn_max_interval to that received max value.

However, this behavior means that conn_max_interval can only decrease,
but never increase. This could potentially make the conditions for
connection parameters narrower over time, causing subsequent
connections failed on some devices. See the issue 847 in bluez
upstream[1]. The patch 806a5198c05987b748b50f3d0c0cfb3d417381a4
(Bluetooth: L2CAP: Fix rejecting L2CAP_CONN_PARAM_UPDATE_REQ) in the
linux-next fixed this by accepting connection parameter
unconditionally. The relavent test procedure is also on the mailing
list[2].

[1] https://github.com/bluez/bluez/issues/847
[2] https://linuxlists.cc/l/15/linux-bluetooth/t/5350289/(patch_v3)_bluetooth:_l2cap:_fix_rejecting_l2cap_conn_param_update_req#post5352326

[Fix]
Backport the from commit 806a5198c05987b748b50f3d0c0cfb3d417381a4 (Bluetooth: L2CAP: Fix rejecting L2CAP_CONN_PARAM_UPDATE_REQ), which currently is in the linux-next.

[1]
https://patchwork.kernel.org/project/bluetooth/patch/20240521143521.1568672-1-luiz.dentz@gmail.com/

[Test Case]
1. Install the kernel with the backported patch
2. Run the following test case in the PTS:
 L2CAP/LE/CPU/BV-02-C
 GAP/CONN/CPUP/BV-05-C

[Where problems could occur]
This essentially revert the behavior of accepting L2CAP connection parameters back to its original state before e4b019515f950b4e6e5b74b2e1bb03a90cb33039 (Bluetooth: Enforce validation on max value of connection interval).

Note that implementing restriction to the conenction parameters may
take greater effort than just adding a few checks in the kernel. The
user space, notably the bluetoothd may also need adjustments[1]. So in
this case, removing the half-done boundary checks in kernel may still
do greater good if there's no plan to make those additional changes.

[1] https://github.com/bluez/bluez/issues/717#issuecomment-1885719058

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